Micro-electronic circuits and other micro-scale devices are generally manufactured from a substrate or wafer, such as a silicon or other semiconductor material wafer. Multiple metal layers are applied onto the substrate to form micro-electronic or other micro-scale components or to provide electrical interconnects. These metal layers, typically copper, are plated onto the substrate, and form the components and interconnects in a sequence of photolithographic, plating, etching, polishing or other steps.
To achieve desired material properties, the substrate is typically put through an annealing process where the substrate is quickly heated, usually to about 200-500° C. and more typically to about 300-400° C. The substrate may be held at these temperatures for a relatively short time, e.g., 60-300 seconds. The substrate is then rapidly cooled, with the entire process usually taking only a few minutes. Annealing may be used to change the material properties of the layers on the substrate. It may also be used to activate dopants, drive dopants between films on the substrate, change film-to-film or film-to-substrate interfaces, densify deposited films, or to repair damage from ion implantation.
As feature sizes for microelectronic devices and interconnects become smaller, the allowable defect rate decreases substantially. Defects result from contaminant particles, so that reducing particle generating elements in the anneal chamber will reduce defects. The temperature uniformity of the wafer is another significant design factor as it affects the crystalline structure of copper or other materials on the wafer. Another consideration is serviceability. It is important to be able to recover or service a chamber as quickly and efficiently as possible.
Various annealing chambers have been used in the past. In single wafer processing equipment, these annealing chambers typically position the substrate between or on heating and cooling elements, to control the temperature profile of the substrate. However, achieving precise and repeatable temperature profiles can present engineering challenges.
In addition, certain materials, such as copper will rapidly oxidize when exposed to oxygen, at temperatures over about 70° C. If the copper or other material oxidizes, the substrate may no longer be useable, or the oxide layer must first be removed before further processing. These are both unacceptable options in efficient manufacturing. Accordingly, another design factor is to isolate the substrate from oxygen, when the substrate temperature is over about 70° C. Since oxygen is of course present in ambient air, avoiding oxidation of copper during annealing also can present engineering challenges. Improved annealing methods and apparatus are needed.